1. Field of the Invention
This invention relates to a dynamic pressure type fluid bearing which maintains the thrust load capability during rotation constant.
2. Description of the Prior Art
In the dynamic pressure type fluid bearing according to the prior art, as shown in FIG. 1 of the accompanying drawings, a cylindrical hole 2 provided in a housing 1 has a cylindrically shaped inner bearing surface 3 for radial load and a bearing surface 4 for thrust load, and a shaft 5 disposed in the cylindrical hole 2 has a cylindrically shaped outer bearing surface 7 for radial load having grooves 6 for generating a dynamic fluid pressure and a convex conical end bearing surface 8 for thrust load. The housing 1 is provided with a communication hole 12 which communicates the inner bearing surface 3 with the upper surface of the housing 1.
Accordingly, when the shaft 5 rotates the grooves 6 force lubricating fluid surrounding the shaft downwardly and the shaft floats upwardly. The communication hole 12 thus opens to a pressure chamber 11, so that the lubricant in the pressure chamber 11 flows out to the upper surface of the housing 1 through the communication hole 12. In this way, the pressure applied to float the shaft 5 can be kept substantially constant.
However, it is technically difficult to accurately provide the communication hole 12 near the boundary 13 between the outer bearing surface and the end bearing surface, and it is therefore difficult to minimize the upward floating movement of the shaft 5. Also, the communication hole 12 is bent and runs deep into the housing 6. Consequently, there exists a high cost for machining the hole 12 and its passages. Further, during stoppage of rotation of the shaft 5, the end bearing surface 8 makes point-contact with the bottom bearing surface 4 and this leads to a great maximum contact surface pressure which in turn may lead to the possibility of an indentation being created in the bottom bearing surface 4.